This application is directed to wireless communications systems, and more particularly to methods and apparatuses for facilitating handovers in wireless communications systems.
A wireless communication network may be deployed over a defined geographical area to provide various types of services (e.g., voice, data, multimedia services, etc.) to users within that geographical area. In a typical implementation, macro access points (e.g., each of which provides service via one or more cells) are distributed throughout a macro network to provide wireless connectivity for access terminals (e.g., cell phones) that are operating within the geographical area served by the macro network. A macro network deployment is carefully planned, designed and implemented to offer good coverage over the geographical region.
As an access terminal roams a geographical area associated with a network, signal conditions for the access terminal within a given cell may deteriorate, whereby the access terminal may be better served by another cell (e.g., access point, base station) in the network. A typical example would be where a mobile subscriber currently served by a first cell moves away from the first access point towards a second cell. It may be desirable for the access terminal to reselect to another cell in idle mode or be handed-over to another cell in active mode.
To facilitate such mobility, an access terminal regularly monitors for signals (e.g., beacon/pilot signals) of nearby cells. These signals are then compared to determine whether the access terminal should remain on its current serving cell or switch to another cell. In practice, one or more parameters may be used to control how aggressively (e.g., under what signal conditions) an access terminal performs searches for other cells. In addition, one or more parameters may be used to control when (e.g., under what signal conditions) an access terminal re-selects to another cell or is handed-over to another cell.
It is desirable for an access terminal to handover from its serving cell to another cell in a timely manner as the access terminal leaves the serving cell coverage, so that the access terminal does not go into outage. In addition, it is also desirable to avoid ping-ponging effects between the serving cell and another cell (e.g., an access terminal handing over back and forth between the two cells). Timely handovers and avoiding ping-pong effects between the two cells can improve network performance by reducing call drops, improving network signaling load, and increasing access terminal battery life.